Diacetylenic and other non-polymeric polyacetylenic compounds have been used as recording layers for optical discs and similar information storage devices. However, the development of a visual image requires exposure at short wavelengths, which excludes more economical and efficient laser imaging, since the polyacetylene compounds are generally incapable of absorbing energy and undergoing polymerization when exposed to light in the region above about 400 nm. Visual images are those images which are clearly recognizable by the human eye and are characterized by high optical contrast in one or more of the red, green and blue portions of the spectrum. By high optical contrast is meant an optical density difference of at least 1.0 between the maximum density and minimum density portions of the image, where optical density is defined as log.sub.10 (1/transmittance) for transmitted light and log.sub.10 (1/reflectance) for reflected light. Such visual imaging is significantly distinguished from prior data recording where image contrast is relatively low and not easily discernable by the human eye or without high magnification. In several cases laser imaging at wavelengths above 400 nm, based on the thermal color change of the polymeric polyacetylenic compound to develop a useful visual image, has been attempted, but it has been found that cumbersome high-output equipment, e.g. argon, metal-vapor or gas lasers and the like are required. Relatively low-output lasers, in the 650-1000 nm wavelength range, fail to imprint on either the polyacetylenes or their polymers, particularly in relatively thick layers required to produce useful visual images as opposed to the relatively thin layers needed for digital data recording. Accordingly, it is the aim of research, with consideration to cost performance and production efficiency, to provide an organic system most suitable for visual imaging and optical data recording, which is imageable at an output energy in the 650-1000 nm wavelength range characteristic of compact semi-conductor diode lasers.
It is an object of this invention to provide a thermochromic compound which answers the above needs and which is visually imageable by a compact semi-conductor laser or similar source of light emanation or by electron beam, and other sources of short wavelength radiation, by a simplified process which achieves high performance and high production efficiency while realizing significant cost savings.
Another object is to provide a visual imaging process involving exposure of a film to a source of energy generated in a wavelength of from about 400 nm and about 1500 nm which process provides the most efficient use of incident energy in an imaging process.
Another object of the invention is to provide an imageable thermosensitive polyacetylene derivative which is directly and visually imageable by light energy generated in wavelengths up to about 1,500 nm.
Still another object is to provide a visually imageable film which is stable to normal UV light exposure.
These and other objects of the invention will become apparent from the following description and disclosure.